Blade sharpener for household use

ABSTRACT

A blade sharpener for grinding a kitchen knife, etc. in which two separate rotary shafts are provided in parallel, at least one whetstone is mounted on each one of the rotary shafts, the circumferential surface of the whetstone forms a grinding surface, the whetstone on one rotary shaft and the whetstone on the other rotary shaft are positionally shifted in the axial direction of the rotary shafts, and the cutting edge of the blade of kitchen knife is ground by moving the blade in the axial direction of the rotary shafts while applying the cutting edge to the grinding surfaces of the whetstones.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a blade sharpener for grinding at home the blade of a cutting tool such as a kitchen knife.

[0003] 2. Prior Art

[0004] In a conventional electric blade sharpeners for household use, a circular disk-form whetstone is mounted on a single rotary shaft connected to the motor and is rotated, and the blade of a cutting tool such as a kitchen knife is sharpened by applying the cutting edge to the circular grinding surface of the rotating whetstone. This structure is disclosed in, for example, Japanese Patent Application Laid-Open (Kokai) No. H9-131649.

[0005] On the other hand, in manual blade sharpeners, the blade of a cutting tool is brought into a blade insertion groove of the sharpener, and the cutting tool is repeatedly moved back and forth so that the cutting edge is sharpened as disclosed in Japanese Utility Model Registration No. 2,547,576.

[0006] In such electric blade sharpeners that use whetstones mounted on a single rotary shaft as described above, the cutting edge of a kitchen knife is sharpened by way of applying the cutting edge to the circular grinding surface of the whetstone. Accordingly, grinding is performed only on one surface of the blade. As a result, there are problems. First, burrs are formed on the other surface of the blade (which is not ground). Accordingly, this other surface must also be lightly ground during finishing process. Furthermore, since the whetstone is mounted on a single rotary shaft, and grinding is performed by the circular grinding surface of this whetstone, the grinding that is done while moving the kitchen knife is performed by the same whetstone. As a result, the grinding conditions are not varied while moving the kitchen knife.

[0007] In the above-described manual blade sharpener, circular whetstones are mounted on supporting shafts that are provided parallel to the direction in which the blade insertion groove extends; and it is necessary to employ bearing members that hold both ends of each one of the supporting shafts. As a result, spaces for the bearing members are required, and thus the whetstones cannot be provided so as to be in contact with the end of the blade insertion groove, and a certain distance generates between the end of the blade insertion groove and the whetstones. Some knifes, however, cannot be sharpened by such a blade sharpener. In particular, there are substantially two types of knives: in one type the blade has a constant thickness for its entire length, and in another type the blade has an area, near the handle, that is larger in thickness than other portions. When a knife that has, near the handle, an area that is thicker than other portion is sharpened by the above-described manual sharpener, since the blade insertion groove is small in width, such a thicker portion of the blade is not brought into the blade insertion groove. As a result, a portion of the blade that is positioned between the end portion of the blade insertion groove and the whetstones does not make contact with the whetstones and is not ground.

SUMMARY OF THE INVENTION

[0008] Accordingly, the present invention is to provide a grinding apparatus for household use that efficiently grinds and sharpens a cutting tool such as a kitchen knife.

[0009] One object of the present invention is to provide an electric blade sharpener which, by performing grinding simultaneously on both sides of the cutting edge of a cutting tool such a kitchen knife, scissors, etc. while being moved, makes it possible to sharpen the cutting tool by means of a one-stroke operation, i.e., merely by moving the cutting tool one time in one direction, without any need to apply the cutting edge to the whetstone many times.

[0010] Another object of the present invention is to provide a cutting tool sharpener which, using a plurality of whetstones, makes it possible to perform finishing sharpening of a cutting tool by a one-stroke operation with, for instance, a coarse whetstone and a finishing whetstone in combination without any need to apply the cutting edge to the whetstones repeatedly.

[0011] Still another object of the present invention is to provide a cutting tool sharpener that sharpens even a cutting tool that has a thick portion near the handle.

[0012] The above objects are accomplished by a unique structure of the present invention for a an electric blade sharpener in which a whetstone is mounted on a rotary shaft that is rotated by the motive force of a motor; and in the present invention:

[0013] two separate rotary shafts are provided in parallel,

[0014] at least one whetstone is mounted on each one of the rotary shafts,

[0015] the circumferential surfaces of the whetstones form the grinding surfaces of the respective whetstones,

[0016] the whetstone on one rotary shaft and the whetstone on the other rotary shaft are positionally shifted in the axial direction of the rotary shafts, and

[0017] a cutting tool is sharpened by moving the cutting tool in the axial direction of the rotary shafts while applying the cutting tool (or the cutting edge thereof) to the grinding surfaces of the respective whetstones.

[0018] Furthermore, in the present invention, the whetstone on one rotary shaft and the whetstone on the other rotary shaft partially overlap between the two rotary shafts. In addition, the whetstones have a cylindrical shape, and the grinding surfaces are at right angles with respect to the planar or flat portions of the whetstones.

[0019] The whetstone on at least one of the rotary shafts may have a truncated cone shape, and this whetstone is installed so that the smaller diameter side of this cone shape whetstone faces in the direction in which the cutting tool is moved during the grinding process.

[0020] Furthermore, the corner of each one of the whetstones which is between the planar portion and the grinding surface and faces the direction in which the cutting tool is moved to be ground during the grinding process of the cutting tool is beveled.

[0021] In the present invention, two whetstones can be mounted on each rotary shaft.

[0022] In the present invention, the whetstones that are lined up in the direction in which the cutting tool is moved for grinding are provided so that the whetstones on the downstream side of the movement for grinding of the cutting tool are provided with finer grinding surfaces so as to grind the cutting edge of the cutting tool smoother than the whetstones on the upstream side do.

[0023] Furthermore, two whetstones mounted on each one of the rotary shafts are provided so that the whetstone on the downstream side of the movement for grinding of the cutting tool is provided with a finer grinding surface so as to grind the cutting edge of the cutting tool smoother than the whetstone on the upstream side does.

[0024] Furthermore, the whetstones can be mounted sleeve elements of same configuration, and these sleeve elements having whetstones are fastened to the rotary shafts. The sleeve elements of the same configuration having whetstones thereon are respectively fastened to the rotary shafts so that the sleeve elements are positionally shifted in the axial direction.

[0025] In the present invention, in addition, the whetstones on both rotary shafts respectively are rotated in a direction in which the grinding surfaces rub the cutting tool upward during grinding process.

[0026] The rotary shafts are rotated in the same direction, and the motor used in the present invention is an alternating-current motor.

[0027] The above objects are further accomplished by a unique structure of the present invention for a cutting tool sharpener in which the blade of a cutting tool is brought into a blade insertion groove and the grinding is performed by moving the cutting tool; and in this sharpener, a heel end receiving section is provided at one end of the blade insertion groove, and this heel end receiving section is formed so that its width is larger than the width of the blade insertion groove that is formed continuously to the heel end receiving section. The heel end receiving section is provided adjacent to where the handle of a cutting tool is positioned when the blade of the cutting tool is brought into the blade insertion groove.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a perspective view of the main body of the cutting tool sharpener according to the present invention;

[0029]FIG. 2 is a perspective view of a part of the interior of the sharpener main body;

[0030]FIG. 3 is a perspective view of the whetstone box;

[0031]FIG. 4 is a perspective view of the whetstone box seen from the bottom;

[0032]FIG. 5 is a perspective view of the inside of the whetstone cover;

[0033]FIG. 6 is a perspective view of the sharpener with the whetstone cover removed;

[0034]FIG. 7 is a top view of the sharpener with the whetstone cover removed;

[0035]FIG. 8 shows the manner of a whetstone arrangement;

[0036]FIG. 9 is a perspective view of whetstones and a sleeve element;

[0037]FIG. 10A is an enlarged front view of the tubular body, and FIG. 10B is a sectional view taken along the line 10B-10B in FIG. 10A;

[0038]FIG. 11 is an enlarged perspective view of the stopper device;

[0039]FIG. 12 is an overall perspective view of the sharpener of the present invention;

[0040]FIG. 13 is a perspective view of the interior of the sharpener;

[0041]FIG. 14 shows the belt transmission mechanism;

[0042]FIG. 15 is another overall perspective view of the sharpener of the present invention;

[0043]FIG. 16 is a perspective view of the sharpener of the present invention seen from the bottom;

[0044]FIG. 17 is a front view of the sharpener with the cover mounted;

[0045]FIG. 18 is a top view of the sharpener with the cover mounted;

[0046]FIG. 19 is a perspective view of the sharpener having a heel end receiving section; and

[0047]FIG. 20 shows a knife having a thick heel end.

DETAILED DESCRIPTION OF THE INVENTION

[0048] Embodiments of the grinding apparatus or sharpener for cutting tools of the present invention will be described below with reference to the accompanying drawings. The description will be made on a sharpener for a kitchen knife (merely called “knife” below).

[0049] The sharpener comprises a sharpener main body 1 shown in FIG. 1, a whetstone box 2 shown in FIG. 3, and a cover 3 shown in FIG. 18.

[0050] The whetstone box 2 is detachably attached to the sharpener main body 1. The interior of the whetstone box 2 with the whetstone cover 4 removed is shown in FIGS. 6 and 7. Two separate rotary shafts 5 and 6 are provided parallel to each other inside the whetstone box 2 by being supported at their respective end portions.

[0051] A first whetstone 7 and a third whetstone 8 are mounted on one rotary shaft 5, and a second whetstone 9 and a fourth whetstone 10 are mounted on the other rotary shaft 6. When a knife is ground, the knife is moved so that the first whetstone 7 first contacts the cutting edge of the knife, the second whetstone 9 next contacts the cutting edge, the third whetstone 8 next contacts the cutting edge, and then the fourth whetstone 10 contacts the cutting edge at last.

[0052] The respective whetstones 7, 8, 9 and 10 have a cylindrical shape; and in each one of the whetstones, the corner between the planar or flat portion and the circumferential surface that constitutes a grinding surface of the whetstones is beveled, so that the corner has an inclined surface 11.

[0053] The first whetstone 7 and second whetstone 9 are formed from the same material and have the same roughness; and these whetstones have a coarseness of, for example, #120 and perform rough grinding. The third whetstone 8 and fourth whetstone 10 have a finer grain; and these whetstones have a coarseness of, for example, #180 and perform finishing grinding so that they grind the cutting edge smoother than the first and second whetstones 7 and 9 do. The third whetstone 8 and fourth whetstone 10 are made of the same material.

[0054] In other words, the whetstones, which are lined up in the direction shown by arrow in FIG. 7 in which the knife is moved to be ground during grinding, are provided so that the whetstones 8 and 10 that are on the downstream side of the movement for grinding of the knife have finer grinding surfaces so that they grind the cutting edge of the knife smoother than the whetstones 7 and 9 that are on the upstream side. Furthermore, the whetstones 7 and 8 on the rotary shaft 5 are provided so that the whetstone 8 that is on the downstream side of the movement for grinding of the knife is provided with a finer grinding surface so as to grind the cutting edge of the knife smoother than the whetstone 7 that is on the upstream side, and the whetstones 9 and 10 on the rotary shaft 6 are provided so that the whetstone 10 that is on the downstream side of the movement for grinding of the knife is provided with a finer grinding surface so as to grind the cutting edge of the knife smoother than the whetstone 9 that is on the upstream side.

[0055] The present invention is, however, not limited to the construction as described above. All of the whetstones 7, 8, 9 and 10 can be different in coarseness. In addition, they can be arranged so that grain of the whetstones becomes finer in the order from the first whetstone 7 to the fourth whetstone 10.

[0056] The shape of the whetstones is not limited to a cylindrical shape. The whetstones mounted on at least one of the rotary shafts 5 and 6 can have a truncated cone shape as shown in FIG. 8. In this case, a larger whetstone 12 and a smaller whetstone 13 are used, and the circumferential surfaces of the whetstones 12 and 13 are lined up along a single straight line. In use, the cutting edge of the knife first contacts the larger whetstone 12 and then contacts the smaller whetstone 13; thus as see from FIG. 8, the smaller diameter sides of the cone shape whetstones face in the direction in which the knife is moved or drawn to be ground during the grinding process. As a result, the cutting edge angle can be slightly increased in the finishing stage of the sharpening, thus increasing the strength of the cutting edge.

[0057] As shown in FIG. 7, the left and right side whetstones overlap slightly (at their edge portions) in the center between the two rotary shafts 5 and 6. As a result of this slight overlapping, the angle of the bottom of a substantially V-shaped grinding groove formed by the whetstones on both sides becomes smaller, and the cutting edge is sharply ground.

[0058]FIG. 9 shows the whetstones before mounted on the rotary shafts.

[0059] The whetstones 7 and 8 are not directly mounted on the rotary shaft 5. Instead, the whetstones 7 and 8 are mounted on both ends of a sleeve 14 that has an expanded in diameter portion at the center. The rotary shaft 5 is passed through a hole 15 in the sleeve 14, and the sleeve 14 with the whetstones thereon is fastened in a specified position of the rotary shaft 5. Another sleeve 14 with whetstones 9 and 10 thereon is fastened likewise in a specified position of the other rotary shaft 6. Thus, since the same sleeves with the whetstones mounted thereon can be manufactured in large numbers and appropriately fastened to the rotary shafts, the whetstones can be mounted on the rotary shafts efficiently.

[0060] In the upper surface of the whetstone box 2, a blade insertion groove 16 in which the blade of the knife is inserted and moved or drawn (thus being guided) is formed.

[0061]FIG. 5 shows the inside of the whetstone cover 4, particularly the construction of the blade insertion groove 16. No that the bottom of the blade insertion groove 16 is removed for its the entire length, but bottom portions 17 and 18 are disposed near both ends of the blade insertion groove 16. In other words, the blade insertion groove 16 has no bottom in the area between the bottom portions 17 and 18, thus forming a narrow slit 19.

[0062] The reference numerals 20, 21, 22 and 23 indicate protruding walls that reach the bottom portions 17 and 18. The first whetstone 7 is positioned in the space 24 which is between the bottom portion 18 and the protruding wall 21, the third whetstone 8 is positioned in the space 25 between the protruding wall 21 and the protruding wall 23, the second whetstone 9 is positioned in the space 26 between the protruding wall 20 and the protruding wall 22, and the fourth whetstone 10 is positioned in the space 27 between the protruding wall 22 and the bottom portion 17. Thus, since the circumferential surfaces of the respective whetstones show only slightly for sufficient enough to grind the knife in the respective spaces 24, 25, 26 and 27 inside the blade insertion groove 16, there is no danger that sharpening debris will fly into the surrounding area during use. The sharpening debris drops into the interior of the whetstone box 2 from the respective spaces. The sharpening debris inside the whetstone box 2 can be discharged from a discharge hole 39 (see FIG. 3).

[0063] On the bottom surface of the whetstone box 2 and on the upper surface of the sharpener main body 1, an engaging device used to the secure, in a detachable fashion, the whetstone box 2 on the sharpener main body 1 is provided.

[0064] As shown in FIG. 1, a recess area 28 used for mounting the whetstone box 2 is formed on the upper surface of the sharpener main body 1. This recess area 28 is surrounded on two sides by a sidewall 29 and an end wall 30. As seen from FIG. 7, the sidewall 29 is curved so that this wall opens toward the left as it runs downward in FIG. 7. One side surface 31 of the whetstone box 2 is likewise curved so as to conform to the curvature of this sidewall 29. Accordingly, the sidewall 29 of the sharpener main body 1 and the side surface 31 of the whetstone box 2 make a tight contact with each other, and the end wall 30 of the sharpener main body 1 and the end surface 32 of the whetstone box 2 make a tight contact with each other, so that the whetstone box 2 is securely fitted to the sharpener main body 1, and rattling of the whetstone box 2 never occur during use.

[0065] A guide groove 34 is formed in the bottom surface 33 near the outside portion of the recess area 28. Furthermore, another (second) guide groove (not shown) is also formed so as to face the guide groove 34 so that the sidewall 29 is the bottom of this groove. This (second) facing guide groove is formed by integrally forming an L-shaped part on the sidewall 29. As seen from FIG. 4, projections 35 that engage with the guide groove 34 and the (second) guide groove that faces this guide groove 34 are formed in the bottom surface of the whetstone box 2. When the projections 35 are to be engaged with the guide grooves, the engagement is accomplished by opening the space between the end wall 30 and the end surface 32 of the whetstone box, applying the side surface 31 of the whetstone box to the sidewall 29, and then pressing the whetstone box 2 in this state until the whetstone box 2 contacts the end wall 30.

[0066] A pair of engaging grooves 37 are, as shown in FIG. 1, formed in the bottom surface of the recess area 28 near the front surface 36. Furthermore, as shown in FIG. 4, engaging projections 38 that engage with these engaging grooves 37 are provided in the whetstone box 2. When the whetstone box 2 is attached to the sharpener main body 1, the engaging projections 38 engage with the engaging grooves 37 so that the whetstone box 2 is firmly fastened to the sharpener main body 1.

[0067] The reference numeral 40 in FIG. 1 is a stopper that prevents the mounted whetstone box 2 from moving toward the front side (toward the front surface 36) of the main body 1 and coming loose. The stopper 40 is elastically supported so as to emerge or sink and is attached to the sharpener main body 1 together with the stopper device 41 shown in FIG. 11.

[0068] The reference numeral 42 in FIG. 11 is an anchoring projection that fastens the stopper device 41 to the sharpener main body 1 (another anchoring projection 42 is also disposed on the opposite side (not shown in FIG. 11). The stopper 40 is formed as an integral unit with a knob 43, and a portion between these two portions is elastically supported by a coil spring 44.

[0069] With the structure above, when the knob 43 is pressed downward, it is elastically lowered together with the stopper 40, so that the stopper 40 sinks into the interior of the sharpener main body 1. The upper surface of the stopper 40 has an inclined surface. Accordingly, when the whetstone box 2 is mounted on the sharpener main body 1, the anchoring wall 45 (see FIG. 4) formed on the bottom surface of the whetstone box 2 contacts the inclined surface of the stopper 40 and presses the stopper 40 downward so that the stopper 40 sinks into the interior of the sharpener main body before the whetstone box 2 contacts the end wall 30.

[0070] When the whetstone box 2 is moved in this state toward the end wall 30 so that the whetstone box 2 contacts the end wall 30, the stopper 40 elastically protrudes into the interior of an anchoring recess 46 of the whetstone box 2. The protruding stopper 40 contacts the anchoring wall 45 and prevents the whetstone box 2 from moving. When the whetstone box 2 is to be detached from the sharpener main body 1, the knob 43 is pressed down so that the stopper 40 is caused to sink as described above.

[0071] A motor (not shown in the drawings) is installed in the housing 47 of the sharpener main body 1, and the motive force of this motor is transmitted to the rotary shafts by separable spline shaft couplings via various motive force transmission devices.

[0072] In the shown embodiment, as seen from FIG. 3, spline shaft coupling insertion bodies 48 are attached to the ends of the rotary shafts 5 and 6 on a motive force transmission side of the whetstone box 2. The insertion bodies 48 are respectively provided with integrally formed four teeth 49 so that the insertion bodies are in a cruciform shape. As shown in FIG. 2, tubular bodies 50 that are to be connected to these insertion bodies 48 are provided in the sharpener main body 1, and four grooves 51 are, as seen from FIGS. 10A and 10B, formed inside each one of the tubular bodies 50 so that a cruciform shape is formed. As seen from FIGS. 10A and 10B, the inside surfaces of the respective grooves 51 are, near the insertion openings 52, formed into tapered surfaces 53 along with the inside surfaces of the adjacent grooves. Accordingly, since the insertion openings 52 of the respective grooves are formed so that these openings are widened toward outside, the insertion bodies 48 of the whetstone box 2 can be smoothly inserted into the tubular bodies 50. The attachment of the whetstone box 2 to the sharpener main body 1 is thus facilitated. Furthermore, since the above-described spline shaft couplings are of the type in which the teeth 49 of the insertion bodies 48 are inserted into four grooves 51 that are in a cruciform shape, almost no rattling occurs in the joint portions, and vibration are prevented.

[0073] A guide groove 55 is, as seen from FIG. 1, formed in the upper surface 54 of the sharpener main body 1. This guide groove 55 communicates with the blade insertion groove 16 of the whetstone box 2 when the whetstone box 2 is set on the sharpener main body 1. As seen from FIG. 12, the length of the guide groove 55 substantially extends when it communicates with the blade insertion groove 16 of the whetstone box 2, the knife is stabilized when the blade of the knife is inserted into this long groove.

[0074] As seen from FIG. 12, the guide groove 55 is formed so as to be wider than the width of the blade insertion groove 16 of the whetstone box 2. The vertical cross section of the guide groove 55 is, however, not symmetrical about its center. In other words, the right side inside surface of the guide groove 55 is slanted more than the other side as seen from FIG. 12. Accordingly, the inside surface on the left side is flush to the inside surface of the blade insertion groove 16 of the whetstone box 2.

[0075] Furthermore, the upper surface 54 is formed with a step 56 on the right side of the guide groove 55 in FIG. 1. The height of the upper surface 54 on the front surface 36 side of the step 56 is the same, but the upper surface 54 closer to the back surface (opposite from the front surface 36) is formed lower than the step 56. As a result, when the blade of the knife is inserted into the guide groove 55, the cutting edge of the knife is drawn near side (toward the front surface 36) while being applied to the upper surface 54 on the right side; and when the heel portion of the blade of the knife that is near the handle of the knife comes to contact the step 56, the knife is moved “as is” to the left (in FIG. 1); as a result, the blade naturally comes into the guide groove 55, so that the blade is easily inserted into the guide groove 55. Since one (left side in FIG. 1) inside surface of the blade insertion groove 16 and one (left side in FIG. 1) inside surface of the guide groove 55 are flush to each other, the blade of the knife can easily come into the narrow blade insertion groove 16 when the blade contacts these inside surfaces and draw the knife toward the front, i.e., toward the front surface 36 in the direction of arrow in FIG. 1. Thus, the blade of the knife is ground when moved or drawn into the blade insertion groove 16 from the guide groove 55. Since the guide groove 55 and blade insertion groove 16 are located between the spline shaft couplings, the overall height of the sharpener can be reduced.

[0076] Though the step 56 is provided at the front edge of the top surface 54 of the main body 1 as shown in FIGS. 1 and 6 in the above embodiment, the step 56 can be formed in a position that is further back from the front edge of the top surface 54 as shown in FIGS. 7, 12 and 15.

[0077] Next, the construction that transmits the motive force from the motor to the rotary shafts 5 and 6 will be described.

[0078]FIG. 13 shows the interior of the sharpener main body and the whetstone box attached to the sharpener main body. The motor is not shown in FIG. 3, but it is attached to the bottom of the sharpener main body directly beneath the whetstones 7, 8, 9 and 10.

[0079] As will be described in detail below, a belt transmission mechanism is employed for transmitting the motive force of the motor, and a space that includes the motor and rotary shafts 5 and 6 inside the sharpener main body 1 and a space that includes the belt transmission mechanism are separated by a bearing plate 57.

[0080] The power shaft 58 connected to the motor extends parallel to the rotary shaft 5 and 6, and a power gear 59 is attached to the end of this power shaft 58. As shown in FIG. 14, the shaft hole 66 in the power gear 59 has a substantially circular shape having a flat surface inside, and the power shaft 58 has the same outer circumferential shape, so that rotation of the power shaft 58 is securely transmitted to the power gear 59.

[0081] A first gear 60 and a second gear 61 which are larger than the power gear 59 in diameter are provided side by side above the power gear 59. The power shaft 58 and the first and second gears 60 and 61 are anchored on the bearing plate 57. The first gear 60 is provided together with a coaxial lower pulley 62 that rotates as a unit with this gear 60, and the second gear 61 is provided together with a coaxial lower pulley 63 that rotates as a unit with this gear 61. The power shaft 59 engages with the first gear 60, and the second gear 61 engages with the first gear 60. Thus, the motive force of the power gear 59 is first transmitted to the first gear 60 and to the second gear 61.

[0082] Two upper pulleys 64 and 65 are attached and supported on the bearing plate 57 in positions close to the upper end of the sharpener main body 1. As shown in FIG. 14, two projections 68 are formed on the pulley shaft 67 of the upper pulley 65, and recessed portions 69 into which these projections 68 are fitted are formed in the shaft hole of the upper pulley 65. As a result of this structure, the rotation of the upper pulley 65 is securely transmitted to the pulley shaft 67. The other pulley 64 is in the same configuration as the pulley 65.

[0083] A transmission belt 70 is mounted between the lower pulley 62 and the upper pulley 64, and another transmission belt 71 is mounted between the lower pulley 63 and the upper pulley 65, so that the motive force is transmitted.

[0084] The above-described tubular body 50 of one of the spline couplings is attached to the end of the pulley shaft 67. This tubular body 50 and the insertion body 48 of the corresponding rotary shaft 5 are connected via a round hole (not shown) formed in the end wall 30 so that the rotary shaft 5 is rotated, and the first whetstone 7 and third whetstone 8 are rotated as a unit with the rotary shaft 5. The adjacent upper pulley 64, rotary shaft 6, second whetstone 9 and fourth whetstone 10 are also rotated in the same manner as described above.

[0085] The two rotary shafts 5 and 6 in this construction are rotated in opposite directions, so that the whetstones are rotated in such a direction that the whetstones rub upward over the cutting edge of the knife. The present invention is, however, not limited to this construction, and it goes without saying that the rotary shafts can be rotated in the same direction by way of using a means of additional gears interposed.

[0086] As seen from FIG. 13, there is a space between the two upper pulleys 64 and 65, and a groove 72 is formed in the center of the upper end of the bearing plate 57. Since the guide groove 55 is set in this space and groove 72, the overall height of the sharpener can be reduced.

[0087] Next, a grip section 73 that is used to secure the sharpener in place during use will be described.

[0088] As shown in FIG. 12, the sharpener is set so that the front surface 36 is positioned in front (or near side or in front of the user), and the grip section 73 is held by the left hand of a user so that the grip section 73 is covered by the left hand. As shown in FIG. 15, the side surface 75 of the grip section is slightly rounded and is thus formed so that this surface fits the palm of the hand. Furthermore, a concave end surface 74 is formed in the back of the grip section 73. When the grip section 73 is held by being covered by the hand, the fingertips of the user that protrude from the grip section 73 are bent and applied to the concave end surface 74 so that the sharpener can be held in place. In this case, the thumb is naturally on the upper surface of the grip section 73, and the switch 76 can be operated by slight extension of the thumb. Thus, the operation can be done easily. The grip section 73 protrudes to the side of the sharpener and is formed as a part of the housing 47.

[0089] The motor and electrical devices other than an electrical cord connected to this motor are provided inside the grip section 73. The motor employed is, for instance, an alternating-current motor, and thus a plug and an electrical cord that is connected to the plug are accommodated inside the grip section 73. In a case that the motor is a direct-current motor, then a dry cell is accommodated inside the grip section 73. The mechanism of the switch 76 is also provided in the grip section 73.

[0090]FIG. 16 shows the bottom of the sharpener.

[0091] A cover 77 for the electrical cord storage portion is attached, and a groove 78 that allows the passage of the electrical cord during use is formed. Pawls 79 are integrally formed in the groove 78, so that the cord is held in position in the groove 78 by the pawls 79, and the sharpener is prevented from being lifted upward by the cord. Ventilation slits 80 are formed in the bottom of the sharpener. Heat from the motor escapes through the slits 80. Ventilation windows 81 are formed near the cover 77. Either the ventilation slits 80 or the ventilation windows 81 act to suck in the outside air, while the other acts to discharge heated air. Accordingly, the air inside the sharpener flows in a convection current, so that the cooling effect is heightened.

[0092] As shown in FIGS. 17 and 18, a cover 3 can be attached to the upper surface of the sharpener so as to cover other than the grip section 73. Since the peripheral edge portion 83 (see FIG. 12) of the upper surface 54 of the sharpener main body 1 and the peripheral edge portion 84 of the whetstone box 2 are continuous as shown in FIG. 12, the cover 3 snugly covers the upper surface 54 and the whetstone box 2.

[0093]FIG. 19 shows a cutting tool sharpener formed with a heel end receiving section 85 which has a larger width than the blade insertion groove 16 and is formed continuously at the end of the blade insertion groove 16. The end portions of the rotary shafts 5 and 6 (not shown in FIG. 19) are located on both sides of the heel end receiving section 85. This sharpener shown in FIG. 19 efficiently sharpens a knife 87 that has, as seen from FIG. 20, a thick portion at the heel end 86 of the blade 88. Knives having thick heel ends are mostly forged knives.

[0094] In the sharpener of FIG. 19, when the thick heel end 86 of the knife 87 is set in the heel end receiving section 85, the edge of the blade 88 in front of the heel end 86 is located near the whetstones that are inside the blade insertion groove 16; as a result, the edge of the blade 88 can be ground up to the heel end 86.

[0095] The sharpener shown in FIG. 19 is a motor-operated type as describe above, but it can be a manual sharpener that is not operated by an electric motor.

[0096] In the sharpener shown in FIG. 19, the heel end receiving section 85 is formed in the whetstone box 2; however, the sharpener of the present invention is not limited to one that has a whetstone box and is applicable to a sharpener that has no whetstone box.

[0097] In use, the blade 88 of the knife 87 is inserted in the blade insertion groove 16 with the heel end 86 positioned within the heel end receiving groove 85, and the knife 87 is drawn in the direction shown by arrow in FIG. 19. When the knife is thus drawn, the edge of the blade 88 is ground by the whetstones mounted on the rotary shafts 5 and 6 (not shown) under the whetstone box 2.

[0098] The sharpener in FIG. 19 can be designed so that the whetstone box 2 is 69.5 mm long, and the entire length of the blade insertion groove 16 is, including the heel end receiving section 85, 67.5 mm, the heel end receiving section 85 being 16.5 mm long and its largest width being 17 mm.

[0099] As seen from the above, in the present invention, two separate rotary shafts are provided, at least one whetstone is mounted on each of these rotary shafts, the circumferential surfaces of the whetstones form the grinding surfaces, and the whetstone on one rotary shaft and the whetstone on the other rotary shaft are shifted in the axial direction. Accordingly, both sides of the blade of a cutting tool are simultaneously sharpened, and burrs are not created on only one surface of the blade. Consequently, there is no need for re-grinding the opposite surface of the blade to remove burrs, and the cutting tool is sharpened by a one-stroke operation.

[0100] In the present invention, the whetstone on one rotary shaft and the whetstone on the other rotary shaft partially overlap (at edges) between the two rotary shafts. Accordingly, when the cutting edge of a cutting tool is set between the whetstones and sharpened, the cutting edge is ground while being supported on the circumferential surfaces of the whetstones on both sides, without passing between the whetstones and slipping out below. As a result, grinding is performed easily.

[0101] In the present invention, the whetstones have a cylindrical shape, and the grinding surfaces are at right angles with respect to the planar or flat portions of the whetstones. Accordingly, the blade is sharpened using substantially the entire circumferential surfaces of the whetstones, and sharpening work is performed efficiently.

[0102] In the present invention, the whetstone on at least one of the rotary shafts is a truncated cone shape, and this whetstone is provided so that the smaller diameter side of this cone shape whetstone faces in the direction in which the cutting tool is moved during the grinding process. This means that when a cutting tool is ground by the rotating whetstones while being moved, since the diameter of the initial whetstone that grinds the cutting edge is large, the cutting edge is ground extremely sharply, so that the cutting edge angle becomes smaller; however, as the diameter of the whetstone gradually decreases in the direction in which the cutting tool is moved to be ground, the cutting edge angle gradually shows an increased variation. In other words, the sharpness is somewhat reduced. If the cutting edge of a cutting tool is formed too sharply, the strength of the cutting edge tends to decrease, so that nicks are formed in the blade and so that the cutting edge is bent. Accordingly, the strength of the cutting edge can be maintained by the above structure of the present invention.

[0103] In the present invention, the corners that are between the planar portions and grinding surfaces of the whetstones and face the direction in which the cutting tool are moved to be ground during the grinding process of the cutting tool are beveled or have slant surfaces. Accordingly, it is possible to avoid a situation in which the movement of the blade of the cutting tool is obstructed when heel portion of the blade contacts the whetstones during the movement of the cutting tool.

[0104] Furthermore, in the present invention, when two whetstones are mounted on each rotary shaft, grinding is performed by four whetstones. Thus, the sharpening work is performed efficiently. Since there are two or more whetstones on each side of the blade of a cutting tool, the blade is stably supported during grinding, and the sharpening work is smoothly performed.

[0105] The whetstones that are lined up in the direction in which the cutting tool is moved during grinding are provided so that the whetstones on the downstream side of the movement for grinding of the cutting tool has finer grinding surfaces so as to grind the cutting edge of the cutting tool smoother than the whetstones on the upstream side of the grinding movement of the cutting tool. Accordingly, when the cutting edge is sharpened, rough sharpening is performed first, and then sharpening to a finished surface is performed afterward. Consequently, one-stroke grinding is efficiently performed, and the sharpened surface that is finally sharpened is finished to a smoother finished surface.

[0106] Furthermore, the two or more whetstones on the same rotary shaft are provided so that the whetstone on the downstream side of the movement for grinding of the cutting tool has a finer grinding surface so as to grind the cutting edge of the cutting tool smoother than the whetstone on the upstream side of the grinding movement of the cutting tool. With this arrangement, the initial sharpening and finishing sharpening of both surfaces of the blade of the cutting tool are respectively performed by whetstones with the same rough surfaces and the same finishing surfaces on both sides, it is thus possible to grind the cutting edge of the cutting tool into the same degree of grinding or sharpness on both surfaces of the cutting edge.

[0107] In the present invention, sleeve elements on which the whetstones are mounted are provided on the respective rotary shafts, and these two sleeve elements have the same configuration including the whetstones. Accordingly, sleeve elements that have the whetstones and have the same configuration are respectively provided on both rotary shafts with these sleeve elements being shifted in the axial direction. With this structure, there is no need for work to mount a plurality of whetstones on the rotary shafts one at a time with certain gaps between these whetstones, and the whetstones can be mounted on the rotary shafts merely by attaching the sleeve elements to the rotary shafts. Accordingly, the work required for assembling the sharpener is reduced.

[0108] Furthermore, in the present invention, the grinding surfaces of the whetstones on the rotary shafts are rotated in a direction so as to rub the blade of a cutting tool upward during grinding. This means that the two rotary shafts rotate in mutually opposite directions. In other words, the rotation of the whetstones in the direction in which the whetstones rub upward along the cutting tool is an equivalent to sharpening performed while the cutting tool is moved in the direction of the cutting edge with respect to the sharpening surfaces. Accordingly, no burrs are formed in the cutting edge, and a cutting edge that has both sharpness and strength can be obtained.

[0109] In addition, since the rotary shafts are rotated in the same direction, both surfaces of the blade are ground in opposite directions. This structure is more effective when grinding that produces an especially sharp cutting edge is performed.

[0110] Furthermore, with the use of an alternating-current motor, a strong motive force can be obtained.

[0111] In addition, in the present invention, the heel end receiving section is provided at the end of the blade insertion groove so as to be wider than the blade insertion groove. Accordingly, a cutting tool that has a thick portion in the blade is sharpened up to such a thick portion. In addition, since the heel end receiving section is provided in an area where the handle of a cutting tool that is sharpened is positioned, a cutting tool that has a thick portion in the blade can be efficiently sharpened up to such thick portion. 

1. An electric blade sharpener in which a whetstone is provided on a rotary shaft and is rotated by a motive force of a motor and a cutting tool is sharpened when moved in an axial direction of the rotary shafts while applying a cutting edge of the cutting tool to a grinding surface of the whetstone, wherein: two separate rotary shafts are provided; and at least one whetstone is mounted on each of said two rotary shafts, a circumferential surface of said whetstone forming a grinding surface, and a whetstone on one of said two rotary shafts and a whetstone on another one of said two rotary shafts being positionally shifted in an axial direction of said rotary shafts.
 2. The electric blade sharpener according to claim 1, wherein said whetstone on one of said two rotary shafts and said whetstone on another one said two rotary shafts partially overlap between said two rotary shafts.
 3. The electric blade sharpener according to claim 1, wherein said whetstone is in a cylindrical shape, and the grinding surface is at right angles with respect to a planar portion of said whetstone.
 4. The electric blade sharpener according to claim 1, wherein said whetstone on at least one of said two rotary shafts is in a truncated cone shape and is provided so that a smaller diameter portion of said truncated cone shape whetstone faces in a direction in which said cutting tool is moved in the axial direction of said rotary shafts.
 5. The electric blade sharpener according to claim 1, wherein each one of said whetstones is formed with a beveled surface at a corner between the grinding surface and a planar portion that faces a direction in which said cutting tool is moved during grinding of said cutting tool.
 6. The electric blade sharpener according to claim 1, wherein at least two whetstones are mounted on each one of said rotary shafts.
 7. The electric blade sharpener according to claim 6, wherein said whetstones provided in a direction in which said cutting tool is moved for grinding are arranged so that whetstones on a downstream side of a movement for grinding of said cutting tool is provided with finer grinding surfaces than whetstones on an upstream side.
 8. The electric blade sharpener according to claim 6, wherein said at least two whetstones provided on each one of said rotary shafts are arranged so that a whetstone on a downstream side of a movement for grinding of said cutting tool is provided with a finer grinding surface than a whetstone on an upstream side.
 9. The electric blade sharpener according to claim 6, wherein said whetstones are respectively mounted on sleeve elements that have same configurations and said sleeve elements are provided on said rotary shafts.
 10. The electric blade sharpener according to claim 1, wherein said whetstone is rotated in a direction in which the grinding surface of said whetstone rubs said cutting tool upward during grinding.
 11. The electric blade sharpener according to claim 1, wherein said rotary shafts are rotated in the same direction.
 12. The electric blade sharpener according to claim 1, wherein said motor is an alternating-current motor.
 13. A sharpener for a cutting tool in which a blade of a cutting tool is brought into a blade insertion groove and grinding is performed by moving the cutting tool, said sharpener is provided with a heel end receiving section formed at one end of said blade insertion groove, said heel end receiving section having a width that is larger than a width of said blade insertion groove that is formed continuously to said heel end receiving section.
 14. The sharpener according to claim 13, wherein said heel end receiving section is provided adjacent to where a handle of a cutting tool is located when a blade of said cutting tool is inserted in said blade insertion groove. 